H Wilhelmsson

Current Flow in Ion-Acoustic and Langmuir Turbulence Plasma Interaction

The process of Langmuir and ion-acoustic turbulence interaction due to turbulent bremsstrahlung collisions is considered. It is shown that the ion-sound turbulence excites the Langmuir turbulence even for isotropic particle distributions but for anisotropic ion-sound turbulent waves. The presence of both ion-sound and Langmuir turbulence may lead to the excitation of currents which cause strong magnetic fields.

A New Explanation of the High Effective Temperatures in Pulsar Radioemissions

A new nonlinear process, which can explain the high effective temperatures of pulsar radio emissions, is proposed. It is due to the excitation of low frequency Alfven waves by waves resonantly interacting with the electrons and positrons in the pulsar ultrarelativistic plasma.

A Perturbation Expansion for the Nonlinear Schrödinger Equation with Application to the Influence of Nonlinear Landau Damping

The Bogoliubov-Mitropolsky perturbation method has been applied to the study of a perturbation on soliton solutions to the nonlinear Schrodinger equation. The results are compared to those of Karpman and Maslov using the inverse scattering method to those by Ott and Sudan on the KdV equation and to a recent paper by Pereira and Stenflo.

Repetitive Explosive Instabilities

The saturation of explosive instabilities by third order terms is studied analytically and by means of computer in the coherent phase description. The combined effect of nonlinear frequency shifts and effective nonlinear dissipation is considered. The stabilized explosions are found to be repetitive in general.

On the Stabilization of Explosive Instabilities by Nonlinear Frequency Shifts

This paper presents an analytic solution to the problem of explosive instabilities, including the effects of nonlinear frequency shifts proportional to the squares of the amplitudes. It is found that such frequency shifts may introduce stabilization of the explosive instabilities and may lead to soliton-like solutions in time or to solutions which are periodic in time.

One-dimensional Model for Nonlinear Reflection of Laser Radiation by an Inhomogeneous Plasma Layer

A self-consistent nonlinear analysis is given for the (one-dimensional) problem of laser interaction with a plasma layer. The main process considered is the decay of the laser wave into an ion sound wave and a reflected wave. Nonlinear reflection is shown to be possible even for a linearly transparent layer. The reflection and absorption coefficients are studied as functions of as a function of the level of excitation of the ion sound waves in the plasma. The range of parameters for which the reflection or the heating is maximum is considered.

Excitation of Global Alfvén Modes by Trapped Alpha Particles

It is shown that global Alfven modes can be excited by fusion produced trapped alpha particles due to resonance with the precession drift. The order of magnitude of the transport has been estimated.

Effects of velocity-space loss regions on the alpha-particle distribution function and collisional alpha-particle losses in tokamak reactors

The steady-state distribution function for alpha-particles in the presence of loss regions in velocity space is derived in an analytical form on the basis of the Fokker-Planck equation. The particle losses and the associated energy loss of alpha-particles due to scattering into the loss region are estimated for parameters characteristic of a tokamak reactor.

Computation of Ion-acoustic Wave Excitation and its Anomalous Effects for Double-sided Laser-plasma Interaction

Computer results based on a self-consistent nonlinear analysis are given for the (one-dimensional) problem of laser interaction with a plasma layer. Effects of ion-acoustic wave excitation are studied assuming that the plasma is exposed to incident radiation from two oppositely directed laser beams.

Five Wave Interaction–a Possibility for Enhancement of Optical or Microwave Radiation by Nonlinear Coupling to Explosively Unstable Plasma Waves

A rigorous solution is obtained to the problem of five wave interaction in a plasma medium for the case where two of the waves are transverse electromagnetic waves, whereas the remaining three waves are longitudinal plasma or beam waves. The effects of nonlinear instability are studied in a coherent wave description. As a result enhancement of radiative waves may occur in media of interest to high power laser and present day astrophysical research.